Manufacture of steel



Aug. 10, 1965 A. DAMMER ETAL MANUFACTURE OF STEEL Filed June 17, 1964Jnvenfars;

fll ausf M0054, W/LHELM skzuhw United States Patent Ofiice ilwfllhPatented Aug. 10, 1065 This application is a continuation-in-part of ourco pending application, Serial No. 157,300 filed November 28, 1961, nowabandoned, for Manufacture of Steel.

This invention relates to new and useful improvements in the manufactureof steel. The invention more particularly relates to a process forreducing the hydrogen content of steel melts without the necessity ofvacuum.

Too high a content of hydrogen in steel may adversely affect thecharacteristics of steel, as for example the tendency to flake.

Thus, for example, it is generally considered desirable to reduce thehydrogen content of steel which is to be worked by rolling to below 3.0cu. cm./ 100 grams and to below 2.0 cu. cm./ 100 grams for steel whichis to be worked by forging.

In the past, in order to obtain these low hydrogen contents, it wasnecessary to degas the steelmelt under a high vacuum below 1 torr and aslow as .05 to .3 torr. The vacuum degassing could be effected by passinga stream of molten steel into a vacuum chamber by maintaining a bath ofthe molten steel in a chamber maintained under low vacuum and preferablywhile passing a scavenging gas into or through the steel or the like.Vacuum degasification requires the use of special, expensive vacuumequipment and pumps and often the steel melt treated must be free of aslag covering layer.

One object of this invention is the reduction of the hydrogen content ofsteel melts without the requirement of the application of a vacuum.

A further object of this invention is a simplified process for removinghydrogen from steel which may be combined with the blowing of iron meltsto steel.

These and still further objects will become apparent from the followingdescription read in conjunction with the drawing which diagrammaticallyshows an arrangement for effecting the process in accordance with theinvention.

In accordance with the invention, we have discovered that the hydrogencontent of steel melts may be reduced to a value previously onlyobtainable with a high vacuum degasification by maintaining a bath ofthe molten steel with slag covering the surface thereof and blowing astream of oxygen and .5 to 7% by volume and preferably 1 to by volume,based on said oxygen, of a lower chlorinated or fi'uorochlorinateaialkane against the slag with a velocity suflicient to cause intermixingof the slag and at least the upper portion of the bath.

The term stee as used herein includes any of the known or conventionalsteels, such as alloyed, unalloyed steels, and includes iron melts fromwhich steel is ultimately produced, as for example, molten pig iron.

The slag which covers the surface of the molten steel bath treated inaccordance with the invention may be any known or conventional slag andis generally the conventional slag used in the production of theparticular steel in question.

While the content of the slag is not critical and vdoes not affect thetreatment in accordance with the invention, the slags generally have thefollowing components:

Percent b.w.

CaO 30-65 MnO 5-25 Si0 10-30 Remainder iron oxides, magnesia and, ifany, fluxing means preferably CaF Similarly the thickness of the slaglayer is not critical and is generallythat conventionally found in theproduction of steel, as for example, between 2- and 6 cm.

The chlorine-containing material which is blown against the slag withthe oxygen may be a lower hydrocarbon having all of its hydrogen atomssubstituted with chlorine or chlorine and fluorine. As lowerhydrocarbons, any completely chlorinated or completely fluorochlorinatedhydrocarbon having 4 or less carbons atoms may be used but preferablythe hydrocarbon should not have more than 2 carbon atoms. Carbontetrachloride has proven most preferably but very good results areobtained with hexachloroethane or difluorodichloroethane or the like. Itis also possible to use mixtures of these lower chlorinated orfiuorochlorinated ethanes.

The steel melt with the slag covering is maintained in any sutiablecontainer used in the steel industry, as for example a furnace crucibleor ladle, and the oxygen and chlorine-containing material is blownagainst the surface through any convenient nozzle or lance or nozzles orlances.

It is not necessary to change the lances and nozzles suitable for theprocesses in which oxygen is blown on or into a steel bath, as known inopen hearth or electric furnaces or LD-crucibles. This is true for thedistance between nozzles or lances from the surface of slag surface asknown, the distances vary between 300 and 2000 millimeters.

The blowing should be effected with suflicient velocity to causeintermixing of the slag and at least the upper portion of the melt. Thisvelocity will vary in individual cases depending on the conditions, etc.In general, however, a velocity of at least 200 meters/second,preferably 700800 meters/second, have proven siutable.

The chlorine-containing material and oxygen pass through the samenozzles with the chlorine material being fed into the oxygen stream, asfor example by use of a conventional dosing pump.

It is preferred to blow all oxygen together with the chlorine containingmaterial but it is also possible to blow only a portion of the oxygentogether with said additional material and to blow the remaining portionof oxygen through an additional lance or nozzle or additional lances ornozzles.

The amounts of oxygen may vary over wide limits, as for example between33 and normal cu. meters per metric ton of steel.

The total amount of the chlorine containing material used is alsodependent upon the conditions and the degree of reduction of thehydrogen, content. In general however, amounts of .3 to 1.5 normal cu.meters may be required per metric ton of steel treated.

The treatment in accordance with the invention may be effected at anystage in the production of the steel after the melt has been formed andmay be used in cona hot blast cupola furnace and which had the followingapproximate analysis:

. C 4.0 junction with any of the known or conventlonal meth Si 0.1 ofproducing steel in any of the known 1 COHVeHtlOIlal 5 Mn 0.45 furnaces.P 0.050

Most preferably, however, the treatment 1s combln 5 0,020 with theproduction of SL1 involving an oxygen blow ng To each'of the chargesgooykg lime and 300 g fluorof the melt as for example in the LD processutmzing p spar were added before blowmg. Each of the charges for examplean LD crucible. In accordance with the was blown with oxygen passedthrough the. lance 2, invention, the blowing of the oxygen ontothesurface of d t t f 800 f th 7 bath to convert itto steel may becombined W was mamtame a a ance O mm e h p 1g Hon I surface of the slag.The, gas'pressure 1n the lance was with the treatment 1n accordance withihedl'lVfillllOl'l by maintained. at between 4 and 6V atmosphgres andthe mcludlfdg fi gi g g mammal mtopthe Oxynozzle. velocity of the gasemitted from the lance was gen or e 9 between 700 and 800 meters persecond.

In other steelmakmg processes or open hearth and elec- AS a Lava1 N0ZZ1ewas used the velocity of the g tricfurnace process the treatment iseffected 1n a similar Striking slagrwas Substantially the same The Image%;3; t m in accordance with the invehtion may be outlet diameter of thelance was millimeters, and 1650 e reame t started at a point in thesteel production where the slag 20 2:3 5;'5333$3 5 3g g fisgigg ggig g i:2 layer is replaced by difierent slag layer. If'the treata by meansrofthe dosingpumps at a constant rate ment has been Started before i' lreplaced by Table '1 below shows the total carbon tetrachloride a newSlag, it has been foundpref'ambl3 f subject blown into each of thecharges,the blowing time for each steel after replacement of the slaglayer with a blowing 25 f e charges the analysis f Steel melt producedand with oxygen and the chlorine-containing material in aC- the hydrogencontent as analyze ,b two i di i ll cordance with the invention.takensamples from each charge: a

Table 1 Total abrlnountof Blowing Final analyses of the steel Hzcontent, ppm. I Charge N0. Cvhmgrtgn, 1n miirrlxlilctbs V V p 7 V p C SiMn P '8 Cr Cu A1 Samplel SampleZ 78(18 N1n 27 .09 .22 .36 .014 .020 .30.21. .007 i 1.44 1.4-t .80 (18.5 Nin 25 .08 .25 .37 .007 .024 .12 .13.002 .ss .88 s2 (10 NIIl 25 .10 .19 .35 .012 .024; .18 .005 .96 1. 04

Furthermore, if after the treatment the melt is to be The hydrogencontent analysis was determined by maintained so that it would normallybe in contact with means of a hot aging determinauon at 600 C. (see: theambient air as would occur, for example, by a delay Mitteilungen desKaiser Wilhelm Institut fiir Eisenforin tapping or pouring, it has beenfound preferable to schungl-Vol. XIX (1937). Lfg.8, page 105-112 andmaintain the steel free from contact withrthis ambient Iron and Coal,'15. 8. 1960, page 301-304). air b flowin with an inert gas with orwithout chlorine- In comparison thereto identical melts were blown undery g I n I V a containing material. This is done to prevent a rise 1n thesubstantially identical conditions without the C 31 the hydrogen contentof the melt which could occur, however, the hydrogen content was above4.0 ppm. and through the absorption of hydrogen from the moisture thesteel melt produced had the following analysis:

in the ambient air. Theexpression inert gas does not mean only argon,helium etc., but means all gases which do not affect the bath. 7

7 Thus, for example, waste gas, as for example, blast furnace or hotcupola gas may be used, being blown on the surface of the melt at asuflicient rate to. prevent contact with the air. It has been found thateven a small hydrogen content of, for example about 12% hydrogen in suchgas is not detrimental.

V The following examples are given by Way of illustration and notlimitation:

EXAMPLE 1 An arrangement consisting of an LD-crucible and a lance asshown in FIG. 1 is utilized for treatment. In the drawing theLD-crucible is designated with 1,. the, lance capable of being raisedand lowered is designated with 2. The closing pump 3 has to pump thefluid CC], from a container d by means of a pressure conduit 5 at 6 intothe lance 2 and thereby into a stream of oxygen. 7 is the tapping hole.r

The LD-crucible 1 which had a capacity of 35 metric tons was chargedwith 3 separate charges of pig iron which had been produced fromscr'apiron and coke in EXAMPLE 2 Example 1 was repeated except that the(PS1,; was replaced by the following chlorine containmg materials:

(a) Hexachloroethane (b) Dichlorodifluoroethane '(c) Decachlorobutane Qi (d) Mixtures of the above.

, In each case the hydrogen content of the'melt is re-- duced to below1.6 p.p.m.

EXAMPLE3 Example 1 was further repeated exceptthat the 50% of the slagwas withdrawnafter a blowing period of 14 minutes together with 44liters (10.3 normal cubic meters) CC-l After adding of lZO k-g. lime and.120-lzg. fluo.r-' spar blowing was continued for 17 minutes with theresult that hydrogencontent was 1.8 -p.p.m.

In a steel containing: .12 C, .24 Si, .38 Mn, .014 P, .024 S, .19 Cr,.20 Cu, .008 Al, all percents by weight, in the final analysis.

While the invention has been described in detail with reference tocertain specific embodiments, various changes and modifications whichfall Within the spirit of the invention and scope of the appended claimswill become apparent to the skilled artisan. The invention is thereforeonly intended to be limited by the appended claims or their equivalentswherein We have endeavored to claim all inherent novelty.

We claim:

1. Process for reducing the hydrogen content of steel melts, whichcomprises maintaining a bath of molten steel with slag covering thesurface thereof and blowing a stream of oxygen and .5 to 7% by volume,based on said oxygen, of a member selected from the group consisting oflower completely chlorinated alkanes, lower completely fiuorochlorinatedalkanes, and mixtures thereof, against the slag with a velocitysufiicient to cause intermixing of the slag and the upper portion of thebath for a period of time sufiicient to substantially reduce thehydrogen content of the melt.

2. Process according to claim 1 in which said group member is blown insaid stream of oxygen.

3. Process according to claim 1 in which said group member is utilizedin amount of about 1 to 5% by volume, based on said oxygen. 7

4. Process according to claim 1 in which said group member is C01 5.Process according to claim 1 in which said group member is utilized inamount of .3 to 1.5 normal cu. meters per metric ton of steel treated.

6. Process according to claim 1 in which the bath of molten steel ismaintained at normal pressure.

7. Process according to claim 1 which includes protecting the melt withan inert gas from prolonged contact with moisture-containing ambientatmosphere after said treatment.

8. In a process for blowing iron to steel in which a stream of oxygen isblown against a bath of slag covered molten iron, the improvement forproducing steel with a lowered hydrogen content which compriseseifecting the blowing with a stream of oxygen additionally containing .5to 7% by volume of a member selected from the group consisting of lowercompletely chlorinated alkanes, lower completely fluorochlorinatedalkanes, and mixtures thereof.

9. Improvement according to claim 8 in which said group member ispresent in amount of about 1 to 5% by volume.

10. Improvement according to claim 8 in which said group member is CCl11. Process according to claim 1 which includes removing said slag fromsaid bath of molten steel, covering the surface of said bath of moltensteel with a different slag and continuing said blowing against the newslag.

12. Process according to claim 1, in which said oxygen is blown in atleast two separate streams, at least one of said streams containing saidgroup member.

References Cited by the Examiner UNITED STATES PATENTS 2,068,785 1/37Bain 12 2,770,860 11/56 Webbere 22-2l4 3,046,107 7/62 Nelson et al 75603,060,015 10/62 Spolders et al 75-60 BENJAMIN HENKIN, Primary Examiner.

1. PROCESS FOR REDUCING THE HYDROGEN CONTENT OF STEEL MELTS, WHICHCOMPRISES MAINTAINING A BATH OF MOLTEN STEEL WITH SLAG COVERING THESURFACE THEROF AND BLOWING A STREAM OF OXYGEN AND .5 TO 7% BY VOLUME,BASED ON SAID OXYGEN, OF A MEMBER SELECTED FROM THE GROUP CONSISTING OFLOWER COMPLETELY CHLORINATED ALKANES, LOWER COMPLETELY FLUOROCHLORINATEALKANES, AND MIXTURES THEREOF, AGAINST THE SLAG WITH A VELOCITYSUFFICIENT TO CAUSE INTERMIXING OF THE SLAG AND THE UPPER PORTION OF THEBATH FOR A PERIOD OF TIME SUFFICIENT TO SUBSTANTIALLY REDUCE THEHYDROGEN CONTENT OF THE MELT.